The present invention relates to a seal load inspection apparatus which is installed in or separately provided from a capping unit which drives a rubber plug into a vessel such as vial and then applies a metal cap over the rubber plug and tightens it around the full perimeter while applying a load to the metal cap, and in particular, to such apparatus which allows a seal capacity of the rubber plug to be confirmed by detecting a load acting on the metal cap upon completion of the tightening operation.
A vial which is filled with a medication is sealed, for example, by driving a rubber plug into an opening thereof after it is filled with a content, fitting a cap formed of a metal such as aluminum over the rubber plug and tightening the cap by folding the skirt (lower end) of the cap inwardly.
A sealing load of such a vial depends on the seal capacity of the rubber plug. To achieve a sufficient sealing performance with the rubber plug, the latter must be maintained in an adequately compressed condition. If the tightening operation were performed without a compression of the rubber plug, a failure of obtaining a satisfactory seal capacity results.
Accordingly, it is a general practice that a tightening around the metal cap takes place while a vessel fitted with the metal cap over the driven rubber plug is loaded as by a pressure block. However, the metal cap having its skirt (lower end) folded inwardly in conformity to the outer profile of the vessel may spring back or the folded portion may tend to be restored to its original configuration upon completion of the tightening operation, creating a clearance with respect to the outer surface of the vessel. As a consequence, the rubber plug may be restored due to its own resilience by an amount corresponding to such clearance when the load which has been applied from over the metal cap is released, and the load of the cap which prevails subsequent to the completion of the tightening operation may be diminished from the load applied during the tightening operation. In such an instance, the seal capacity of the rubber plug is likely to be insufficient. Thus, there is a need to detect a load acting on the cap subsequent to the completion of the tightening operation in order to confirm that the rubber plug provides a sufficient seal capacity.
A capping unit which detects a load during a tightening operation which takes place by applying a load from over a cap fitted over a vessel opening or a capping unit which detects a load applied when a cap is driven into a vessel opening is known in the art (see Japanese Laid-Open Patent Publications No. 61-189 and No. 8-58889, for example). In the capping unit disclosed in the first citation (which is referred to therein as a lid clamping device), a load cell is mounted on a cam which elevates a capping head (clamping head), and a load on a roll-on cap as it is tightened is detected in an in-line manner. In the capping unit disclosed in the second citation (which is referred to therein as a capper), a load cell is mounted on a bottle receptacle to detect a load as a cap is driven.
Capping units described in the above patent literature are not constructed in a manner to provide a seal capacity by a rubber plug as it is driven into a vessel, and are therefore not subject to any significant variation in the load at the end of a capping operation. A desired load can be obtained after the end of a capping operation by applying a preset load during the capping operation, and hence, there is no detection of a variation in the load upon releasing the load at the end of the capping step such as a tightening operation.